`print.data.table` with `trunc.cols=TRUE` doesn't wrap the truncated column name list

[ChristopherEeles]

May be related to #1523.

If a user wants to truncate a printed data.table to max 80 characters per line, wouldn't they also want to wrap the list of truncated columns with the same limit? This is currently not the case.

DT <- data.table(
    first_long_column_name=LETTERS[1:5],
    second_long_column_name=letters[1:5],
    third_long_column_name=1:5,
    fourth_long_column_name=LETTERS[1:5],
    fifth_long_column_name=1:5,
    sixth_long_column_name=letters[1:5]
)
print(DT, trunc.cols=TRUE)
##    first_long_column_name second_long_column_name third_long_column_name
## 1:                      A                       a                      1
## 2:                      B                       b                      2
## 3:                      C                       c                      3
## 4:                      D                       d                      4
## 5:                      E                       e                      5
## 3 variables not shown: [fourth_long_column_name, fifth_long_column_name, sixth_long_column_name]

Best,
Christopher Eeles

[MichaelChirico]

Thanks for filing. What's your expected behavior here?

## 3 variables not shown: [fourth_long_column_name, ...]

## 3 variables not shown: [fourth_long_column_name, fifth_long_column_name, 
##                                       sixth_long_column_name]

Something else?

FWIW I am basically fine with not wrapping in this case. Though it would be pretty simple to accomplish with strwrap(). I just don't see the advantage -- could you elaborate on why this improvement is important?

[ChristopherEeles]

Hi @MichaelChirico,

I would expect all output to be truncated at 80 characters per line. I had your second example in mind when I opened the issue, but the first example also seems reasonable.

My specific use case is for a show method where a data.table is a slot in an S4 class. I am grabbing the result of the print statement with capture.output then processing it to tab indent the printed table and colorize it with crayon.

I was surprised when the last item in the captured output wasn't already strwraped with trunc.cols=TRUE. I guess this probably isn't a concern for everyday users of data.table, but it is for developers who want to leverage its efficiency for use in Bioconductor packages, where S4 classes are the norm.

Best,
Christopher Eeles

[tdhock]

I agree, here is a simpler demo of this issue

> print(as.data.table(rbind(1:99)), trunc.cols=TRUE)
      V1    V2    V3    V4    V5    V6    V7    V8    V9   V10   V11
   <int> <int> <int> <int> <int> <int> <int> <int> <int> <int> <int>
1:     1     2     3     4     5     6     7     8     9    10    11
88 variables not shown: [V12 <int>, V13 <int>, V14 <int>, V15 <int>, V16 <int>, V17 <int>, V18 <int>, V19 <int>, V20 <int>, V21 <int>, ...]

would be great to wrap the "88 variables not shown" list to be something like this

> print(as.data.table(rbind(1:99)), trunc.cols=TRUE)
      V1    V2    V3    V4    V5    V6    V7    V8    V9   V10   V11
   <int> <int> <int> <int> <int> <int> <int> <int> <int> <int> <int>
1:     1     2     3     4     5     6     7     8     9    10    11
88 variables not shown: [V12 <int>, V13 <int>, V14 <int>, V15 <int>, 
V16 <int>, V17 <int>, V18 <int>, V19 <int>, V20 <int>, V21 <int>, ...]

[tdhock]

one use case where this would be important is rendering a PDF book, where the text that goes over the right margin is literally not visible.